 Fermentation is another way that cells can convert nutrients into energy that they can use. Fermentation is different from cellular respiration because it's completely anaerobic. It happens without oxygen present. However, it's very similar to what we've already learnt. So, fermentation is kind of like glycolysis plus. We've had a look at glycolysis, so we know that the process occurs in the cytosol. We know that it creates three different things. We get two ATP molecules, which the cell can use straight away. We get some electrons transferred so that we end up with two NADH molecules and two protons or two H plus ions. And we get two molecules of pyruvate. In fermentation, or glycolysis plus, the cell needs to find a way to use up that pyruvate and to access the electrons from the NADH. There are a few different ways that cells can undergo fermentation, two of which you're probably already familiar with. So one is alcohol fermentation, something that we rely on other organisms doing to make bread, beer, wine. And it's done by many different types of bacteria and yeasts. So to do this process, the cell converts pyruvate molecules created in glycolysis into carbon dioxide and a different molecule called acid aldehyde. The acid aldehyde is then combined with NADH and H plus and converted into ethanol and NAD plus. So we've harnessed the energy from that electron transfer and also created alcohol. Another option in fermentation is lactic acid fermentation. And you probably know about this as well from eating cheese or yogurt or maybe working out really hard sprinting before warming up or doing a lot of reps. In this case, the cell uses the pyruvate and NADH and that proton to convert them into a lactate molecule, which is the iron of lactic acid and NAD plus. So in fermentation, it is a lower payoff. We know that glycolysis only creates two ATP out of one glucose molecule compared to the 38 for a whole cell respiration process. So if our organism is using fermentation, it has much higher nutrient energy needs. Some organisms can survive completely without oxygen just by doing fermentation and they're called anaerobes. Other organisms can switch depending on what's available to them so they can do full cell respiration or if not, they can just do fermentation and they're called facultative anaerobes. So that includes yeasts, lots of bacteria types and our muscle cells. Do this when they can't get enough oxygen, perhaps because you've just started sprinting. If they need the energy fast, they'll go straight on to lactic acid fermentation because they can't get enough oxygen immediately and this works for a while and gives us a burst of energy but it can end up in muscle soreness because we then end up with a lot of lactic acid in our cells which needs to be digested again by the cell later on.